Yeah, I agree that they most likely did get the names from the member list, I just think if it wasn't available and someone wanted to to look for passwords on this site, they'd just get the names another way. I could be wrong.
One thing that's interesting to me is that I've never heard of this happening on other sites (although I don't claim to have that kind of knowledge of a lot of forums), and even though it happens here every few months I haven't seen a lot of evidence of accounts being hacked.
Haven't had it happen to my site either - and it is great that vB has the built-in timeout if it does happen. I still think hiding it from guests may help to avoid some future skiddie attacks and save a few future "My account is under attack threads."